Ceramic wiring carriers having a multilayer construction can be produced using what is termed the LTCC (Low-Temperature Co-Fired Ceramic) method. A flexible tape or flexible film, made of a mixture of glass, ceramic, and organic solvents, is used as the initial base.
In a first step for the production of a LTCC wiring carrier, the films are cut for a corresponding number of layers. In a second step, the individual layers are mechanically processed, i.e., adjustment and through-connecting holes (vias) are stamped into the tape layers. In a third step, a via filling pressure is applied, and metallizations are applied by a screen printing process, using a suitable conductive paste. In a fourth step, the individual layers are pressed, and, in a fifth step, sintering takes place at approximately 850° C. to 900° C. During sintering, the LTCC material shrinks by approximately 15% in the z direction. Since about 1995, it has been possible to achieve a shrinkage of almost zero in the x/y direction. In further steps, resistances are applied on the rear side, and the printed conductors on the front side are provided with platinum layers.
Due to the possibility of processing the film layers before the sintering individually and in different ways, LTCC wiring carriers can be realized having many different shapes and constructions. LTCC wiring carriers are suitable, for example, for circuits exposed to high or low ambient temperatures and strong temperature change stress, because the LTCC can also be used as a construction element in the packaging. For example, in the automotive area, LTCC wiring carriers provide an economical and reliable solution for large piece counts. However, the organic materials, incorporated at first into the flexible films or into the printed conductor pastes via expensive intermediate stages for material preparation, are combusted, and thus do not create any value in the part.
Such methods for producing a ceramic multilayer circuit are described in German Patent Reference No. DE 196 15 787 A1 and German Patent Reference No. DE 198 17 359 A1. German Patent Reference No. DE 196 38 195 A1 discloses a dielectric paste for use in the production of ceramic multilayer circuits.